Conventionally, to know a relative position between a plurality of vehicles, a device capable of directly measuring a distance to a vehicle such as a millimeter wave radar is arranged and used, and functions of line traveling and collision warning are realized by control information of a vehicle position and vehicle to vehicle communication of communicating the vehicle position by wireless means. In these functions, the relative position is important information, and in a case where the distance cannot be directly measured by the millimeter wave radar or the like, the relative position can be calculated by exchanging respective positions by vehicle to vehicle communication or the like. However, in a case where different errors occur in the respective positions, all the errors occur as errors of the relative position.
Therefore, in a case of obtaining a relative position with a second vehicle using vehicle to vehicle communication, PTL 1 discloses a method of calculating a position with high accuracy in three or more vehicles by aggregating satellite vehicle information such as pseudo distances and the like observed in the vehicles in one vehicle that serves as a reference vehicle, and positioning and calculating the relative position. Further, PTL 2 discloses a technology enabling calculation of a relative position even with a small number of satellite vehicles by transmitting motion information of vehicles together with a plurality of pieces of satellite vehicle information. By using these methods, the relative position between vehicles can be calculated with high accuracy.